Realizing High Thermoelectric Performance below Phase Transition Temperature in Polycrystalline SnSe via Lattice Anharmonicity Strengthening and Strain Engineering

We report the high thermoelectric performance of p-type polycrystalline SnSe obtained below the phase transition temperature by harnessing Pb doping and introducing Sn vacancies. The enhanced carrier concentration induced by Pb doping and introducing Sn vacancies contributes to enhancements of electrical conductivity and power factor of polycrystalline SnSe. We demonstrate that the lattice anharmonicity is strengthened by Pb substitution and Sn vacancies through forming weaker bonds. We find that Pb substitution introduces huge stress field in the interior of the SnSe grains. The thermal conductivity can be greatly reduced by lattice anharmonicity strengthening and applying huge stress field. The lattice thermal conductivity is reduced to as low as 0.18 W m–1 K–1 in the Sn0.92Pb0.03Se sample at 773 K. As a result, a remarkable high ZT of ∼1.4 was achieved at 773 K in the Sn0.93Pb0.02Se sample through lattice anharmonicity strengthening and strain engineering.